watchOS 5.1 (build 16R591) is an official Apple over-the-air update for the Apple Watch Series 3 (38mm, LTE), released on 2018-10-30T17:21:18Z. The update package is 817.95 MB. This is a delta (partial) update that requires 4.0.1 already installed. This update is no longer signed by Apple, meaning it can no longer be applied on-device through Settings.

Payload file: 90264d1a8d4994c4b5a97eb76cb831b6680d8510.zip.